This invention relates generally to the field of phacoemulsification and more particularly to irrigation/aspiration (“I/A”) systems used during phacoemulsification.
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of the lens onto the retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens.
When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an IOL.
In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, a thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an artificial lens.
A typical ultrasonic surgical device suitable for ophthalmic procedures consists of an ultrasonically driven handpiece, an attached cutting tip, and irrigating sleeve and an electronic control console. The handpiece assembly is attached to the control console by an electric cable and flexible tubings. Through the electric cable, the console varies the power level transmitted by the handpiece to the attached cutting tip and the flexible tubings supply irrigation fluid to and draw aspiration fluid from the eye through the handpiece assembly.
The operative part of the handpiece is a centrally located, hollow resonating bar or horn directly attached to a set of piezoelectric crystals. The crystals supply the required ultrasonic vibration needed to drive both the horn and the attached cutting tip during phacoemulsification and are controlled by the console. The crystal/horn assembly is suspended within the hollow body or shell of the handpiece by flexible mountings. The handpiece body terminates in a reduced diameter portion or nosecone at the body's distal end. The nosecone is externally threaded to accept the irrigation sleeve. Likewise, the horn bore is internally threaded at its distal end to receive the external threads of the cutting tip. The irrigation sleeve also has an internally threaded bore that is screwed onto the external threads of the nosecone. The cutting tip is adjusted so that the tip projects only a predetermined amount past the open end of the irrigating sleeve.
In use, the ends of the cutting tip and irrigating sleeve are inserted into a small incision of predetermined width in the cornea, sclera, or other location. The cutting tip is ultrasonically vibrated along its longitudinal axis within the irrigating sleeve by the crystal-driven ultrasonic horn, thereby emulsifying the selected tissue in situ. The hollow bore of the cutting tip communicates with the bore in the horn that in turn communicates with the aspiration line from the handpiece to the console. A reduced pressure or vacuum source in the console draws or aspirates the emulsified tissue from the eye through the open end of the cutting tip, the cutting tip and horn bores and the aspiration line and into a collection device. The aspiration of emulsified tissue is aided by a saline flushing solution or irrigant that is injected into the surgical site through the small annular gap between the inside surface of the irrigating sleeve and the cutting tip.
One possible complication associated with cataract surgery is anterior chamber collapse following an occlusion break. Occlusion of the phacoemulsification tip can occur when a piece of lens material fully covers the distal aspiration port. When an occlusion occurs, vacuum can build in the system aspiration line so that when the occlusion eventually breaks, a sudden surge occurs, drawing fluid and lens material out of the eye and into tip aspiration port. When fluid is draw out of the eye faster than it can be replaced, the eye can soften and collapse.
One way to reduce surge after an occlusion break is to reduce the compliance in the aspiration system. By reducing compliance, vacuum build-up during an occlusion is reduced. However, as flexible tubings are used to connect the handpiece to the surgical console, there will always be some compliance in the aspiration system.
Another prior art method involves increasing the size of the irrigation line. While not addressing the size of any post-occlusion fluid surge directly, a larger irrigation line allows for large irrigation fluid flows, so that any vacuum build-up in the eye is more easily quenched, thereby reducing the risk of anterior chamber collapse. Larger irrigation lines, however, can make the handpiece more difficult to hold and control.
Therefore, a need continues to exist for a simple and reliable irrigation/aspiration system that reduces fluid flow surges.